The present invention relates to a two-stroke cycle internal combustion engine that is suited for use in a portable power working machine, for instance, and in particular to a two-stroke cycle internal combustion engine which is capable of minimizing the quantity of so-called blow-by, i.e., the quantity of unburned air-fuel mixture that is discharged from the engine with the exhaust gases.
An ordinary two-stroke cycle internal combustion engine which is conventionally used in a portable power working machine, such as a chain saw, is constructed such that an ignition plug is disposed at the head portion of the cylinder, and an intake port, scavenging ports and an exhaust port, which are to be opened and closed by a piston, are provided at the trunk portion of the cylinder. In such a two-stroke cycle internal combustion engine, one cycle of the operation of the engine is accomplished by two strokes of the pistonxe2x80x94the piston does not perform strokes which are exclusively assigned to the intake of an air-fuel mixture or the exhaust of combustion gases.
More specifically, during each ascending stroke of the piston, an air-fuel mixture is introduced from the intake port into the crank chamber disposed below the piston. When the piston descends, the air-fuel mixture in the crank chamber is pre-compressed, producing a compressed gas mixture, which is then utilized for exhausting the combustion gas from the exhaust port; i.e., the compressed gas mixture is blown into a combustion actuating chamber, which is disposed above the piston, so as to expel the combustion gas toward the exhaust port. (Although it might variously be called a combustion chamber, an actuating chamber, a cylinder chamber, etc., these chambers are generically referred to in the present specification as xe2x80x9cthe combustion actuating chamber.xe2x80x9d) In other words, since the scavenging of the combustion gas is effected by making use of the gas flow of the air-fuel mixture, the unburned air-fuel mixture is more likely to be mingled into the combustion gas (exhaust gas), thereby increasing the quantity of so-called blow-by, i.e., the quantity of unburned air-fuel mixture that is discharged from the engine into the atmosphere with the exhaust gases. Because of this, the two-stroke cycle internal combustion engine is not only inferior in fuel efficiency but also disadvantageous in that a large amount of undesirable components, such as HC (unburned components in a fuel) and CO (incomplete combustion components in a fuel), are included in the exhaust gas as compared with a four-stroke cycle engine Therefore, even if the two-stroke cycle engine is small in capacity, the influence of these undesirable components on environmental contamination should not be disregarded.
With a view to solving these problems, various proposals have been made for two-stroke cycle internal combustion engines in which air is introduced into the combustion actuating chamber prior to the introduction of air-fuel mixture so as to scavenge the combustion gas (see, for example, Japanese Patent Unexamined Publications H9-125966 and H5-33657). However, even with these proposals, it is difficult to sufficiently reduce the quantity of blow-by. Additionally, the layout and structure of the parts of the engine, including the air-fuel mixture passageway and air passageway, are not sufficiently sophisticated, thus causing the engine to increase in overall size. Therefore, the two-stroke cycle internal combustion engines proposed in the aforementioned publications might be further improved for the purpose of mounting them on a portable power working machine.
A so-called binary scavenging system is now adopted in the conventional Schnxc3xcrle-type scavenging two-stroke internal combustion engine, wherein a pair of scavenging ports are located symmetrically with respect to a longitudinal plane that bisects the exhaust port, and a portion of the scavenging flow of the air-fuel mixture that is blown out of the pair of scavenging ports impinges against a stationary inner wall of the cylinder (cylinder bore). A so-called quaternary scavenging system comprising two pairs of scavenging portsxe2x80x94i.e., an additional pair of scavenging ports is further added to the aforementioned binary scavenging systemxe2x80x94is also known.
However, even in the two-stroke cycle internal combustion engine having a quaternary scavenging system, it is impossible to sufficiently minimize the quantity of so-called blow-by even if, according to the method conventionally proposed, the scavenging of combustion gas is performed by introducing air prior to the introduction of air-fuel mixture into the combustion actuating chamber as in the case of the two-stroke cycle internal combustion engine having a binary scavenging system. Furthermore, the layout and structure of the parts of the engine, including the air-fuel mixture passageway and air passageway, are not sufficiently sophisticated, thus causing the engine to increase in size. Therefore, there remains a need for the two-stroke cycle internal combustion engine having a quaternary scavenging system to be further improved for uses such as in portable power working machines
The present invention has been made to solve the aforementioned problems. It is, accordingly, an object of the present invention to provide a two-stroke cycle internal combustion engine having a quaternary scavenging system, which is capable of minimizing the quantity of blow-by, capable of improving the fuel consumption and power of the engine, capable of reducing the content of undesirable components in the exhaust gas, and capable of rationally and compactly arranging the parts of the engine.
With a view to attaining the aforementioned objects, a two-stroke cycle internal combustion engine, which includes a cylinder and a piston defining a combustion actuating chamber and a crankcase below the piston and defining a crank chamber, has a quaternary Schnxc3xcrle-type scavenging system that includes an exhaust port, a pair of first scavenging passageways communicating the combustion actuating chamber with the crank chamber and disposed closer to the exhaust port, and a pair of second scavenging passageways communicating the combustion actuating chamber with the crank chamber and disposed farther from the exhaust port. The first scavenging passageways are disposed symmetrically with respect to a longitudinal plane that bisects the exhaust port. Similarly, the second scavenging passageways are disposed symmetrically with respect to the longitudinal plane. An air passageway is arranged for introducing air into the first scavenging passageways, and an air-fuel mixture passageway is provided for introducing an air-fuel mixture from an air-fuel-generating device into the crank chamber. The scavenging system is configured such that during a descending stroke of the piston, the exhaust port opens first, a first scavenging port formed at a downstream end of each first scavenging passageway opens after the exhaust port opens, and a moment later, a second scavenging port disposed at a downstream end of each second scavenging passageway opens, whereby air is introduced into the combustion actuating chamber from each first scavenging port prior to the introduction of the air-fuel mixture into the combustion actuating chamber from each second scavenging port.
In an advantageous construction of the two-stroke cycle internal combustion engine according to the first embodiment, a communicating passageway communicating with the downstream end of the air-fuel mixture passageway communicates the crank chamber with the combustion actuating chamber via an air-fuel mixture-feeding port provided at the downstream end of the communicating passageway. The air-fuel mixture-feeding port is configured to open substantially simultaneously with the second scavenging ports.
In another preferred embodiment of the two-stroke cycle internal combustion engine according to the present invention, the air passageway and the air-fuel mixture passageway are provided respectively with a check valve.
In yet another preferred embodiment of the present invention, the pair of first scavenging passageways are combined at a place close to the crank chamber, and end portions of said pair of first scavenging passageways which are disposed close to the crank chamber are contracted.
In the first embodiment of a two-stroke cycle internal combustion engine according to the present invention, the air passageway and the air-fuel mixture passageway are preferably arranged adjacent each other, one above the other, and the air-fuel mixture blown out of the air-fuel mixture-feeding port of the communicating passageway is designed to be blown toward a combustion chamber of the combustion actuating chamber.
In a specific preferred embodiment of the present invention, the air-fuel-generating device is a carburetor, which includes portions of the air passageway and the air-fuel mixture passageway, each such portion having a throttle valve. The throttle valves are interlocked with each other.
In a two-stroke cycle internal combustion engine of the present invention as described above, the ambient air is inducted through the air passageway into the first scavenging passageway and the crank chamber so as to be held therein during the ascending stroke of the piston, and the air-fuel mixture fed from the air-fuel-generating device is inducted into the air-fuel mixture passageway, the crank chamber and the second scavenging passageway so as to also be held therein.
When the air-fuel mixture inside the combustion actuating chamber disposed above the piston is ignited and burns, the piston is pushed downwardly due to the generation of combustion gas. In the descending stroke of the piston, an exhaust port opens first, and when the piston is further descended, a first scavenging port provided at a downstream end of each first scavenging passageway is opened so as to allow air which has been held in the first scavenging passageway and the crank chamber and compressed by the descending of the piston to be blown out of the first scavenging port into the combustion actuating chamber disposed above the piston, thereby allowing the combustion gas to be pushed toward the exhaust port by the air.
When the piston further descends after the first scavenging port has been opened, second scavenging ports at the downstream ends of the second scavenging passageways and the air-fuel mixture-feeding port are opened a moment after the first scavenging ports have opened (in other words, for example, 10 degrees later in terms of the crank angle), thereby allowing the relatively condensed air-fuel mixture existing inside the air-fuel mixture passageway to be blown from the second scavenging ports and from the air-fuel mixture-feeding port into the combustion chamber of the combustion actuating chamber. The air-fuel mixture thus blown out is prevented from being mixed with the combustion gas due to the presence of an air layer that has been introduced therein in advance from the first scavenging ports, thereby allowing the air-fuel mixture to circulate in the vicinity of the combustion chamber.
Thereafter, throughout almost all of the scavenging period, air is introduced through the first scavenging ports into the combustion actuating chamber, while throughout almost all of the scavenging period, the air-fuel mixture is introduced, through the second scavenging ports and the air-fuel mixture-feeding port, into the combustion actuating chamber.
Thusly, in the first embodiment of the internal combustion engine of the invention, the first scavenging passageways are employed exclusively for the passage of air, while the second scavenging passageways are employed exclusively for the passage of air-fuel mixture, and the second scavenging ports and the air-fuel mixture-feeding port are opened a moment later after the first scavenging ports open, thereby allowing a relatively condensed air-fuel mixture to be blown out of the second scavenging ports and the air-fuel mixture-feeding port toward the combustion chamber of the combustion actuating chamber, and preventing the air-fuel mixture thus blown out from being mixed with the combustion gas due to the presence of an air layer that has been introduced therein in advance. The air-fuel mixture circulates in the vicinity of the combustion chamber and hence promotes a stratified combustion. As a result, the quantity of blow-by is reduced to a minimum, and at the same time, the air-fuel mixture can be easily ignited, thus making it possible to improve combustion for greater fuel economy and to reduce the content of undesirable components in the exhaust gas.
Furthermore, since the air passageway and the air-fuel mixture passageway are arranged side by side, the parts of the engine can be rationally and compactly arranged, thus making it possible to easily mount the engine on a portable power working machine.
In addition, since the feeding of air is conducted not through an outside pump but through a piston pumping, the entire structure of the engine can be simplified and the manufacturing cost of the engine can be reduced.
A two-stroke cycle internal combustion engine according to a second embodiment is a quaternary schnxc3xcrle-type scavenging system and has a pair of first scavenging passageways communicating the combustion actuating chamber with a crank chamber and disposed closer to the exhaust port, and symmetrically with respect to a longitudinal plane which bisects the exhaust port and a pair of second scavenging passageways communicating the combustion actuating chamber with the crank chamber and disposed farther from the exhaust port and located symmetrically with respect to the longitudinal plane that bisects the exhaust port. An air passageway introduces air into the first scavenging passageways, and an air-fuel mixture passageway introduces an air-fuel mixture from an air-fuel-generating device into the crank chamber.
During the descending stroke of the piston and at least in the initial stage of the scavenging period during which a first scavenging port formed at a downstream end of each first scavenging passageway and a second scavenging port formed at a downstream end of each second scavenging passageway are opened, only air is allowed to be introduced into the combustion actuating chamber from the first and second scavenging ports.
In the second embodiment of the engine, the capacity of each second scavenging passageway is preferably made larger than the capacity of each first scavenging passageway, so that during the descending stroke of the piston, air is allowed to be introduced into the combustion actuating chamber from the second scavenging port prior to the introduction of the air-fuel mixture and at the same time, a relatively large quantity of air is allowed to be introduced into the combustion actuating chamber from the first scavenging port over a longer period of time as compared with a period of time in which air is introduced from the second scavenging port.
It is advantageous in this case that only air is allowed to be introduced through the first scavenging ports into the combustion actuating chamber throughout the entire scavenging period.
In the second embodiment of the two-stroke cycle internal combustion engine, it is advantageous to include a communicating passageway communicating the crank chamber with the combustion actuating chamber at the downstream end of the air-fuel mixture passageway, such that during the descending stroke of the piston, the exhaust port opens first, the first scavenging ports and the second scavenging ports are then opened, and a moment later, an air-fuel mixture-feeding port provided at the downstream end of the communicating passageway is opened, and such that air is introduced into the combustion actuating chamber prior to the introduction of the air-fuel mixture.
Other two-stroke cycle internal combustion engines according to the present invention advantageously may include the following features: (1) During the descending stroke of the piston, the exhaust port opens first, and then, the first scavenging ports and the second scavenging ports are simultaneously opened; (2) The air passageway is provided with a check valve; (3) A single air outlet port disposed at the downstream end of the air passageway is communicated with both the first scavenging passageway and the second scavenging passageway, and the air outlet port is provided with a single check valve; (4) The pair of first scavenging passageways are combined at a place close to the crank chamber; (5) The end portions of the pair of first scavenging passageways which are disposed close to the crank chamber are contracted; (6) The air-fuel mixture passageway is provided with a check valve; (7) The air passageway and the air-fuel mixture passageway are arranged side by side; (8) The air-fuel mixture blown out of the air-fuel mixture-feeding port of the communicating passageway is blown toward a combustion chamber of the combustion actuating chamber; (9) The air-fuel-generating device is a carburetor, which includes portions of the air passageway and the air-fuel mixture passageway, each being provided with a throttle valve, and the throttle valves being interlocked with each other.
In operation of a two-stroke cycle internal combustion engine according to the second embodiment described above, the external air is drawn in through the air passageway into the first scavenging passageways, the second scavenging passageways and the crank chamber so as to be held therein in the ascending stroke of the piston, and the air-fuel mixture fed from the air-fuel-generating device is drawn into the air-fuel mixture passageway and the crank chamber so as to be also held therein.
When the air-fuel mixture inside the combustion actuating chamber disposed above the piston is ignited and burns, the piston is pushed downwardly due to the generation of combustion gas. In the descending stroke of the piston, the air and air-fuel mixture existing inside the crank chamber, the first scavenging passageways and the second scavenging passageways are compressed. The exhaust port opens first, and when the piston has further descended, the first scavenging ports provided at downstream ends of the first scavenging passageways and the second scavenging ports provided at downstream ends of the second scavenging passageways are opened simultaneously. In the initial stage of the scavenging period during which the first and second scavenging ports are opened, only the air compressed by the piston and residing in the first and second scavenging passageways is allowed to be introduced into the combustion actuating chamber from the first and second scavenging ports.
Subsequently, when the piston has descended further, the air residing in the first scavenging passageway is allowed to be continuously introduced into the combustion actuating chamber from the first scavenging ports (preferably, the air is introduced throughout the entire scavenging period), whereas the introduction of air into the combustion actuating chamber from the second scavenging ports ends. Namely, when a certain period of time has elapsed after the second scavenging ports have been opened, since all of the air inside the second scavenging passageways will have already been introduced into the combustion actuating chamber from the second scavenging ports, the air-fuel mixture that has been pre-compressed in the crank chamber is introduced, following the aforementioned introduction of air from the second scavenging ports via the second scavenging passageways into the combustion actuating chamber until the scavenging period ends.
When the piston further descends after the first and second scavenging ports have been opened, the air-fuel mixture-feeding port is opened a moment after the first and second scavenging ports have opened (eg., 10 degrees later in terms of the crank angle), thereby allowing the relatively condensed air-fuel mixture existing inside the air-fuel mixture passageways (and the crank chamber) to be blown from the air-fuel mixture-feeding ports into the combustion chamber of the combustion actuating chamber until the scavenging period ends, thereby allowing the air-fuel mixture to circulate in the vicinity of the combustion chamber.
In the case of the quaternary scavenging type two-stroke internal combustion engine according to the first embodiment wherein the first scavenging port is exclusively used for air and the second scavenging port is exclusively used for an air-fuel mixture, the combustion exhaust gas is allowed to remain in the vicinity of the inner wall of the cylinder which is located opposite to the exhaust port. By contrast, in the two-stroke internal combustion engine of the second embodiment, since only air is allowed to be introduced into the combustion actuating chamber from both of the first and second scavenging ports in the initial stage of the scavenging period, the combustion exhaust gas is substantially not allowed, due to this air, to remain in the cylinder, including a portion in the vicinity of the inner wall of the cylinder which is located opposite to the exhaust port, but is caused to be pushed toward the exhaust port so as to be discharged therefrom At the same time, an air layer is caused to be formed between the combustion exhaust gas and the air-fuel mixture that is introduced later into the combustion actuating chamber from the air-fuel mixture-feeding port and the second scavenging ports. Therefore, due to the air layer, a mixing between the air-fuel mixture and the combustion exhaust gas can be effectively prevented, thereby realizing an almost complete stratified scavenging.
In the second embodiment, the first scavenging passageways are employed exclusively for the passage of air, while the second scavenging passageways are employed exclusively for the passage of the air-fuel mixture only after the initial stage of the scavenging period during which the second passageways supply air. The air-fuel mixture-feeding port opens a moment later after the first scavenging ports and the second scavenging ports open, thereby allowing a relatively condensed air-fuel mixture to be blown out of the second scavenging ports and the air-fuel mixture-feeding port toward the combustion chamber of the combustion actuating chamber after a middle stage of the scavenging period, thereby preventing the air-fuel mixture thus blown out from being mixed with the combustion exhaust gas due to the presence of an air layer that has been previously introduced, thus enabling the air-fuel mixture to circulate in the vicinity of the combustion chamber and hence, promoting a stratified combustion. As a result, the quantity of blow-by can be reduced, and at the same time, the air-fuel mixture can be easily ignited, thus making it possible to improve the fuel consumption and to reduce the content of undesirable components in the exhaust gas.
Further, since the air passageway and the air-fuel mixture passageway are arranged side by side, the parts of the engine can be rationally and compactly arranged, thus making it possible to easily mount the engine on a portable power working machine.
Furthermore, since the feeding of air is conducted not through an outside pump, but through a piston pumping, the entire structure of the engine can be simplified and the manufacturing cost of the engine can be reduced.